Secondary Seal for Floating Roof Tanks

2 Secondary Seals

 A Secondary Seal is an auxiliary rim sealing systeminstalled above the Primary Seal on an External Floating Roof TankEFRT and IFRT Its primary purpose is to provide an additional barrierbetween the floating roof and the tank shell thereby further reducinghydrocarbon vapour emissions VOC minimizing product evaporation losses andpreventing the ingress of rainwater dust and debris into the annular rimspace The secondary seal follows the movement of the floating roof whileaccommodating shell outofroundness weld projections thermal expansion andoperational deflection When installed together with a primary seal itsignificantly improves sealing efficiency and helps storage tanks comply withenvironmental regulations such as EPA 40 CFR Part 60 Secondary sealsalso protect the primary seal from direct sunlight wind rain and mechanicaldamage extending its service life

Main standards and guidelines governing Secondary sealsare below 

API Standards

API 650  Design requirements for External Floating Roof Tanks Appendix C and Internal Floating Roof Tanks Annex H

API 575  Inspection practices for atmospheric and lowpressure storage tanks including rim seal systems

API 653  Inspection repair alteration and replacement of rim seals

API RP 545 Lightning protection requirements secondary seals must not interfere with electrical bonding or bypass conductors

Environmental Regulations

US EPA 40 CFR Part 60 NSPS

US EPA 40 CFR Part 63 NESHAP

European VOC regulations

Local regulations such as OISD guidelines India where applicable

 

The main Secondary Sealcategories are

2a Compression PlateSecondary Seal

Description

Springloaded galvanized or stainlesssteel compressionplates press the seal fabric against the tank shell One of the most commondesigns

 

Typical Application

External Floating Roof Tanks EFRT 

 

Guideline  Standard

API 650 Appendix C API 575 API 653 EPA 40 CFR Part6063

 

Material of Construction MOC  

The Compression Plates can be use pregalvanize sheet orStainless Steel AISI 304  The Vapour Barrier can be Nylon Fabric coated withNBR   Nylon Fabric coated with PU NylonFabric coated with Viton  PTFEcoated Fiberglass special chemical service asper Customer Requirement The Wiper Tip  Wiper Seal can be use made from NBR PVC NBR Viton  PVC Nitrile Blend extrudedProfile 

2 Weather Shield Secondary Seal

Description

Metallic weather shield with resilient seal underneathprotects the primary seal from rain UV dust and wind

Typical Application

External Floating Roof Tanks EFRT

Guideline  Standard

API 650 API 575

Material of Construction MOC   The Weather ShieldSecondary Seal Plates can be use pregalvanize sheet or Stainless Steel AISI304 

2b Wiper Tip Resilient Blade Seal

Description

Flexible polyurethane nitrile rubber or reinforcedelastomer blade wipes against the shell to seal small gaps

Typical Application

External Floating Roof Tanks EFRT   Internal Floating Roof Tanks IFRT

 Guideline  Standard

API 650 API 575

Material of Construction MOC  

Flexible polyurethane  PVC nitrile rubber or reinforcedelastomer blade